1. Field of the Invention
The present invention relates to an apparatus and method for cleaning a device and in particular to an apparatus and method for cleaning a screen or stencil in a screen or stencil printer.
2. Background of the Invention
In typical surface-mount circuit board manufacturing operations, a stencil printer is used to print solder paste onto a circuit board. Typically, a circuit board having a pattern of pads or some other, usually conductive, surface onto which solder paste will be deposited is automatically fed into the stencil printer and one or more small holes or marks on the circuit board, called fiducials, is used to properly align the circuit board with the stencil or screen of the stencil printer prior to the printing of solder paste onto the circuit board. Once the circuit board has been properly aligned with the stencil in the printer, the circuit board is raised to the stencil, solder paste is dispensed onto the stencil, and a wiper blade (or squeegee) traverses the stencil to force the solder paste through apertures in the stencil and onto the board. As the squeegee is moved across the stencil, the solder paste tends to roll in front of the blade, which desirably causes mixing and shearing of the solder paste so as to attain desired viscosity to facilitate filling of the apertures in the screen or stencil. The solder paste is typically dispensed onto the stencil from a standard cartridge such as that manufactured by SEMCO Corporation.
In some prior art stencil printers, any excess solder paste remaining under the squeegee after it has fully traversed the stencil, remains on the stencil when the squeegee is returned to its initial position for printing on a second circuit board. In some prior art screen printers, a second squeegee is used that moves across the stencil in the direction opposite to that of the first squeegee. The first squeegee and the second squeegee are used on alternating boards to continually pass the roll of solder paste over the apertures of a stencil to print each successive circuit board. Usually, as the squeegees pass the solder paste over the apertures minute amounts of solder paste seep through the apertures to accumulate at the bottom side of the stencil. This presents various problems such as the solder paste being inadvertently disposed on unintended areas of the circuit board. Also, as the solder paste hardens, it complicates the alignment procedure of a circuit board with the stencil. Therefore it is desirable to remove the excess solder paste at the bottom of the stencil.
According to one prior art stencil printer, after several prints, a stencil wiper apparatus in the stencil printer that is situated near the vicinity of the stencil moves beneath the stencil from one end to the other end. As the stencil wiper apparatus moves beneath the stencil, it wipes off excess solder paste at the bottom of the stencil. The prior art stencil wiper apparatus will now be described with respect to FIG. 1. The prior art stencil wiper apparatus 10 comprises a paper supply roller 12 containing a roll of paper, a pair of paper guide rollers 14, a hollow solvent tube 16 with numerous holes along its length and a vacuum plenum 18. During a cleaning session, a paper winder motor 22 rotates the paper supply roller 12, which passes paper through the pair of paper guide rollers 14. Between the paper guide rollers 14 there is the hollow solvent tube 16 that is filled with solvent by a solvent pump (not shown) which causes the solvent tube 16 to squirt solvent through its numerous holes onto the paper as it passes by the solvent tube. The solvent impregnated paper is passed to a vacuum plenum 18, which holds the paper in place as the stencil moves over the paper thereby cleaning the stencil. It is desired to provide a method and apparatus for applying solvent onto a material that is an improvement to the stencil wiper apparatus described above.
According to one aspect of the invention, a printer for printing a viscous material at predetermined positions forming a pattern on a substrate comprises a frame, a device located in an area of the frame and having a number of perforations arranged to form the pattern, a support apparatus mounted to the frame that supports the substrate in a printing position beneath the device, a viscous material dispenser mounted to the frame that contains a viscous material to be printed on the substrate, a device cleaner including a cleaning material dispenser that dispenses a cleaning material to clean a surface of the device, a solvent bath that contains a solvent, and a rotatable bar that rotates in the solvent bath, the rotatable bar being in contact with the cleaning material to apply the solvent in the solvent bath to the cleaning material.
Other features may include one or more of the followings: a motor that rotates the rotatable bar; a reciprocating apparatus mounted to the frame, the device cleaner mounted to the reciprocating apparatus, the reciprocating apparatus moves the device cleaner from one end of the device to another end, and the device cleaner is configured to clean the device as the reciprocating apparatus moves the device cleaner; the device cleaner further comprises a solvent tank that holds a reservoir of solvent, and a first pump that fills the solvent bath with solvent from the solvent tank; the device cleaner further comprises a plurality of ports to drain excess solvent in the solvent bath, and a second pump to return the excess solvent to the solvent tank; the motor is a speed variable motor, and a speed of the variable motor determines an amount of solvent that is applied to the paper; and a vacuum plenum to hold the cleaning material while the device makes contacts with the cleaning material to wipe excess viscous materials from the device.
In another aspect of the invention, the printer for printing a viscous material at predetermined positions forming a pattern on a substrate comprises a frame, a device located in an area of the frame and having a number of perforations arranged to form the pattern, a support apparatus mounted to the frame that supports the substrate in a printing position beneath the device, a material dispenser mounted to frame that contains a viscous material to be printed on the substrate, a device cleaner having a cleaning material that contacts the device to wipe excess material from the device and means for evenly applying a solvent to the cleaning material.
Other features may include one or more of the followings: the solvent applying means includemeans for dispensing the cleaning material, means for containing the solvent and means for rotating in the solvent containing means, the rotating means applying the solvent to the cleaning material as the cleaning material passes the rotating means; the solvent applying means further comprises means for maintaining a predetermined level of solvent in the solvent containing means; and the rotating means further comprises means for varying a quantity of solvent applied to the cleaning material.
In another aspect of the invention, a method for printing a viscous material at predetermined positions forming a pattern on a substrate using a device, the method comprising placing the substrate beneath the device in a printing position, dispensing the viscous material on the device, applying the viscous material across the device to fill the number of perforations in the device to form the pattern on the substrate, wiping excess viscous material from the device wherein the step of wiping includes rotating a bar in a solvent container to draw solvent to the rotating bar, applying the solvent to a cleaning material using the rotating bar, and wiping off excess viscous material on a surface of the device using the cleaning material.
Other features may include one or more of the followings: maintaining a predetermined level of solvent in the solvent container; and varying a speed of the rotating bar to vary an amount of solvent to be applied to the cleaning material.